Mapping the electrical activity of the epicardium provides important mechanistic and diagnostic information. This has traditionally been done by an array of electrodes placed in a "sock" wrapped around the heart. "Optical mapping" is a new technique which involves the use of voltage sensitive dyes and optical and electronic circuitry. It was developed to study the electrical activity of excitable cells and has major advantage over traditional methods in that it can record transmembrane voltages with a high degree of resolution. This technology has been successfully applied to small regions of epicardium. We propose to develop the technology for global cardiac electrophysiological optical mapping. We intend to use fiber-optic technology coupled with a new detector design and enhanced software technology to generate whole-heart optical maps. The proposed technology is responsive to the National Heart Lung and Blood Institutes' solicitation on the topic and will result in a very versatile device to image the heart's electrical activity that will be of great use to a broad spectrum of biomedical scientists in universities, and in the pharmaceutical and medical device industries. PROPOSED COMMERCIAL APPLICATIONS: There is a market for several dozen optical mapping units a year to be sold as research systems for universities. We anticipate this market will be significantly larger once this technology has achieved the acceptance of the pharmaceutical and pacemaker/defibrillator device industry.